For example, a pressurized water reactor (PWR) uses light water as a reactor coolant and a neutron moderator, fills a reactor core with not-boiled, high-temperature and high-pressure water, sends the high-temperature and high-pressure water to a steam generator to generate steam by heat exchange, and sends the steam to a turbine generator to generate power.
A reactor vessel used for such a pressurized water reactor is constructed of a reactor vessel main body and a reactor vessel cover mounted on the reactor vessel main body so that a reactor-internal structure can be inserted in the reactor vessel, and the reactor vessel cover is openable/closable with respect to the reactor vessel main body. Further, when the reactor vessel cover is mounted on the reactor vessel main body in a freely attachable/detachable manner, a stud bolt is caused to penetrate an outer peripheral flange of the reactor vessel cover and is screwed in and embedded in an upper outer peripheral flange of the reactor vessel main body, and a nut is screwed with the stud bolt with tension acting on the stud bolt, so that fastening is performed.
Such a fastening and loosening device is disclosed in Patent Literature 1 described below. A device disclosed in Patent Literature 1 performs work using a bolt tensioner.